Our long term objective is to gain as complete a picture as we can of the multiplication of poliovirus in HeLa cells. In this way we hope to accomplish two ends: (1) to provide a model for the growth of all picornaviruses and, where possible, a model for aspects of the growth of all RNA viruses and (2) to learn whatever the virus will tell us about macromolecular synthesis in mammalian cells. Four major projects are contemplated: (1) We plan to test the hypothesis that poliovirus RNA is translated into a single polypeptide which is cleaved by proteases to form the functional viral proteins. Use of viral RNA in cell-free systems to direct the formation of viral proteins and isolation and characterization of the enzymes which carry out the cleavages are the major goals in this study. Analysis of in vivo events will also be continued. (2) We will characterize an apparent deletion mutant of poliovirus which appears to be a defective, interfering particle. We will try to understand how it can interfere with the growth of standard virus. (3) We will attempt to understand how poliovirus is able to inhibit host RNA synthesis and determine if the viral RNA polymerase has any relation to the cell RNA polymerase. (4) We will attempt to isolate and study poliovirus conditional, lethal mutants.